Wow, an embarrassment of opportunities and a willingness to travel for them.
OK, based on the little I have heard, read, seen, and done, I recommend
A .308 bolt action with as long a barrel as available.
Combination rail that will accept both peep sight and scope; front globe sight base.
That will get you into NRA Long Range in the any rifle-iron sight, any rifle-any sight, and Palma events; plus F-T/R shooting off a bipod instead of sling, coat, and glove. Ranges generally the longest available at the site, 1000 yards where possible. Palma at 800, 900, 1000 iron sight. Discussions at
http://www.long-range.com/forums/
Outside NRA it will get you into "practical-tactial" shooting at ranges as long as you can estimate for sight settings. See Zak's reports. Also, USPSA/IPSC is doing some MOR (Manually Operated Rifle) shooting, a lot of which falls into that category, only faster.
The Brits shoot .308 at 1200 yards but that is very demanding on gun, ammo, and user. In the USA that is getting into monster magnum territory, about which I know little except what I read. The .338 Lapua with a 16.2 gram bullet at 905 mps (250 gr 2968 fps) is a baseline of the breed. If you are target shooting at 1200 yards, that big bullet will be blown 41 inches by a 5 mph crosswind .
If you are "sniping" with one of those and a zero at 1000 yards, you will be about ten inches high and low, respectively, at 975 and 1025 yards.
The main component of Long Range shooting, given an accurate rifle and decent technique, is wind judgement. If at unknown distances, add in range determination.
An NRA Long Range match is shot on paper targets which are pulled and marked for hit location and score every shot. You know what you are doing at all times and can correct for wind, light, ammo, and other variables.
Other shoots may be conducted on steel targets which a spotter can see swing or bullet splash for hits.
Solitary shooting at ranges beyond 200-300 yards is difficult, it is hard to tell what you are doing. I have shot on a steel gong at 600 yards and can hear the bullet hit, and then look for the bullet splash mark through rifle scope or spotting scope. But if I miss, where was I off?
I find it enough of a challenge to shoot F-T/R with .308 or .223 off a bipod at 600 to 1000 yards. The other stuff is more demanding.